Silicon carbide is expected to be a material in next generation semiconductor devices. Silicon carbide has excellent physical properties in which a bandgap is approximately three times that of silicon, breakdown electric field strength is approximately ten times that of silicon, and thermal conductivity is approximately three times that of silicon. It is possible to achieve a semiconductor device in which a loss is low and a high-temperature operation is possible by using these characteristics.
A metal oxide semiconductor field effect transistor (“MOSFET”) using silicon carbide has an operation mode called a reverse conduction state in addition to a typical operation mode. In the typical operation mode, a drain electrode is positively biased with respect to a source electrode, and thus a current flows from the drain electrode toward the source electrode. On the other hand, in the reverse conduction state, the drain electrode is negatively biased with respect to the source electrode, and a current flows from the source electrode toward the drain electrode. In the reverse conduction state, a built-in diode of the MOSFET is turned on, and thus a current flows.
The built-in diode of the MOSFET is a pn-junction diode. In the reverse conduction state, holes are injected to a drift layer from a source electrode side, and electrons are injected to the drift layer from a drain electrode side. A stacking defect from an electric potential in the drift layer may grow due to recoupling energy of the holes and the electrons which are injected to the drift layer. When the stacking defect grows in the drift layer, on-state resistance increases. This problem is referred to as conduction deterioration. The reliability of the MOSFET deteriorates due to the conduction deterioration.